Advance of technology has created greater demand for higher power quality on electronic devices (such as central processors, graphic processors, hard disk drivers and the like). Unstable input power quality causes unstable output power quality of a power supply. The unstable power could cause malfunction of an electronic device, or even cause instant failure of the electronic device in serious situation, thus not only the data during operation may be lost or damaged, also the electronic device may have structural damage.
To avoid abrupt failure of the power supply that might cause unrecoverable damage, nowadays most motherboards require the power supply to provide status information (commonly called PG (Power Good) signal) to perform management and control. In the event that the motherboard receives abnormal status information it starts actions of load reduction, such as lower air fan spinning speed, stop power supply to idled electronic devices or the like to avoid rapid dysfunction of the power supply, meanwhile the motherboard proceeds orderly shutdown of the electronic devices in operation. Please refer to FIG. 1 for conventional power supply architecture. It generally includes a judgment module 17 connecting electrically to a rectification output unit 16 or the secondary side of a transformer 13 of a power supply 1 to receive power to perform status judgment. But external power has to go through a multi-stage circuit (such as a rectification filter unit 11, power factor correction unit 12, primary side of the transformer 13 and the like) to reach the rectification output unit 16 or secondary side of the transformer 13, response time for judgment usually is too late, hence abnormal condition of the external power source 10 cannot be notified instantly to the motherboard 3. To address this issue, some techniques have been proposed to focus on the front end circuit (i.e. the rectification filter unit 11, power factor correction unit 12 or the like) at the primary side of the transformer 13 in the power supply 1 to make inspection result to more match the input end status of the power supply. However, the input end of the power supply usually is at a higher voltage level, but not all electronic elements can withstand high voltage. Moreover, the power supply 1 does not always get DC input. In the event that the power supply 1 gets AC input, a multi-stage filter circuit must be added to the judgment module to eliminate noise signals. This makes the circuit more complex, and transmission of the multi-stage circuit also makes response time longer to result in delay notification. In addition, different AC frequencies also could cause inaccuracy of judgment result. On the other hand, the conventional method for judging status of the power supply merely has one judgment spot, in the event that a slight change happens to the external power source 10, an abnormal signal is output so that it is easily to erroneously judge the failure of the external power source 10.